Shares in General Growth Properties Inc., the second-biggest U.S. mall owner, fell as much as 6.7 percent in New York trading Monday morning after a newsletter report that Simon Property Group Inc. may abandon a takeover bid for its smaller rival.

Indianapolis-based Simon is unlikely to move ahead with its buyout offer because of antitrust concerns, the REIT Newshound reported Sunday night, citing sources it didn’t identify. Simon has concluded that an attorney for Chicago-based General Growth who handles antitrust issues wasn’t dealing in “good faith,” the newsletter said, citing one of the sources.

Simon spokesman Les Morris and General Growth spokesman David Keating didn’t immediately respond to requests for comment.

General Growth fell 4.1 percent to $16.05 as of 11:49 a.m. in New York Stock Exchange composite trading, and sank to as low as $15.61 earlier MOnday. The shares have jumped 71 percent since Feb. 15, the day before Simon made public a $10 billion offer to buy the company out of bankruptcy. General Growth dismissed the bid as too low and instead plans to exit bankruptcy with financing from a group led by Brookfield Asset Management Inc.

“GGP shares were priced based on some sort of topping from Simon,” said Benjamin Yang, an analyst with Keefe, Bruyette & Woods in San Francisco. “Based on this news, it seems less likely that Simon will come back with an offer higher than the $15-a-share proposal from Brookfield.”

General Growth filed the biggest real estate bankruptcy in U.S. history almost a year ago after amassing $27 billion in debt making acquisitions. Simon’s bid would have given equity investors about $9 a share and paid unsecured creditors in full.

Simon has been preparing a new offer for General Growth, a person with knowledge of the plan told Bloomberg News last month.